go to start, control panel, display, desktop, ensure your Position button, right hand side, is set to stretch not tile.
you might also ensure your system is clean:
what is your current antivirus?
Click Start, Run and in the box enter:
msinfo32
Click OK, and when the System Summary info appears, click Edit, Select All (Ctrl-A), Copy (Ctrl-C) and then paste (Ctrl-V) the information back here in your next reply.
You can edit out any personal information.
Download, install, update and do full scan with these free malware detection programs:
Malwarebytes (MBAM): http://www.malwarebytes.org/products/malwarebytes_free
SUPERAntiSpyware: (SAS): http://www.superantispyware.com/
Remove all found, reboot, and run again until scans run clean, these can be removed afterwards if you so choose.